In various kinds of processing apparatuses, such as a cutting apparatus and a polishing apparatus, a processing operation is carried out with processing water supplied to a work during the processing thereof so as to improve the quality of a processed product. For example, in a cutting apparatus 50 adapted to carry out a cutting operation by making a rotary blade 18, which is rotated at a high speed, cut into a work, for example, a semiconductor wafer W as shown in FIG. 4, cutting water is supplied to inflow portions 23, and a cutting operation is carried out with the cutting water, i.e. processing water supplied from a cutting water supply nozzle 20 to contact portions of the semiconductor wafer W and rotary blade 18. The removing of chips occurring during the cutting operation is also done with the cutting water injected from an injection portion 21 onto the wafer W.
The pure water is used as such cutting water in some cases. However, since the pure water has a high specific resistance value (resistivity), static electricity occurs due to the friction thereof against the semiconductor wafer W, so that the semiconductor wafer W is readily charged. Especially, when the work is a semiconductor wafer W, the quality of a final product lowers greatly due to the loading thereof with the static electricity. Therefore, it is necessary that the occurrence of static electricity be prevented by reducing the specific resistance value of the pure water, and that the wafer W be de-electrified.
Under the circumstances, the occurrence of static electricity is prevented by increasing the specific resistance value of the pure water by mixing carbon dioxide with the pure water, and using the conductivity-increased processing water in practice just as in the processing water generating apparatus disclosed in, for example, JP-A-2001-30170.
On the other hand, when the concentration of the carbon dioxide increases to cause the acidity of the pure water to become high, the rotary blade 18 is corroded to cause the lifetime of the same to lower, or a bonding pad formed on the semiconductor wafer is corroded to cause the quality of a final semiconductor chip to lower. Therefore, in the invention disclosed in the publication referred to above, a means for maintaining the specific resistance value of the pure water at a proper level by controlling a flow rate thereof by regulating a valve is provided.
It has been recognized that, in order to carry out, for example, the cutting of a semiconductor wafer, a proper specific resistance value permitting the prevention of the charging of the work with static electricity and the corroding of the rotary blade and bonding pad is in a very narrow range of 0.5 MΩ.cm to 2.0 MΩ.cm. However, in order to set and maintain the specific resistance value in such a range, it becomes necessary that the flow rate be regulated with a high accuracy by using an expensive fine control valve. Therefore, it is difficult to set the specific resistance value to a desired level. Moreover, an expensive fine control valve has to be used, so that the cost of the apparatus increases to a high level. Such problems are problems encountered in a cutting apparatus, and also problems common to processing apparatuses using processing water.
Consequently, the problem of a processing operation using processing water is to develop a means capable of setting the specific resistance value of the processing water to a desired level by an economical method.